It's a cool Monday morning in October 1972, and the Belken County Homicide Squad is dealing with a dead body found in an abandoned car in the middle of a cotton field. Lieutenant Detective Rafe Buenrostro and the four other men making up the squad are accustomed to corpses, even though they live and work in a mostly rural area of South Texas along the Mexican border.The bloody scene at the Kum Bak Inn is a different story, though, and one that is impossible to get used to: three men—including one of their own—slaughtered so brutally that their faces, arms, legs and even genitalia have been completely severed from their bodies. Two witnesses spared this horrific death are able to provide first-hand descriptions of the killers: three Mexican nationals, armed with machine guns, driving a cream-colored, four-door Oldsmobile...